The present invention relates to a copier, facsimile apparatus, printer or similar image forming apparatus.
An image forming apparatus includes a developing unit using either a developing liquid, which consists of a carrier liquid and toner dispersed therein, or a dry powdery developer containing at least toner. Japanese Patent Laid-Open Publication Nos. 7-209922, 7-152254 and 7-239615. For example, each teach a developing unit using a dense, viscous developing liquid that consists of an insulative liquid and toner densely dispersed therein. This kind of developing liquid is directed toward the size reduction of the developing unit.
The above-mentioned Laid-Open Publication No. 7-209922, in particular, discloses a developing unit of the type developing a latent image formed on an image carrier with a developing liquid containing charged toner particles. The developing unit has a high toner content and viscosity as high as 100 mPa.s to 10,000 mPa.s. Developing means feeds the developing liquid to the surface of the image carrier via a conductive developer carrier.
It is a common practice with an image forming apparatus using a developing liquid to remove, with a cleaning device, the liquid remaining on a photoconductive element or image carrier or an intermediate image transfer body after image transfer. The intermediate image transfer body is another image carrier to which a toner image is transferred from the photoconductive element. The toner image is transferred from the intermediate image transfer body to a paper sheet or similar recording medium. Typical of the cleaning device is a cleaning blade formed of, e.g., urethane rubber or similar elastic material. The cleaning blade cleans the surface of the image carrier with its edge contacting the image carrier. A cleaning roller formed of, e.g. an elastic foam material is also known in the art. The cleaning roller is located upstream of the cleaning blade in the direction of rotation of the image carrier in such a manner as to rub the surface of the image carrier, thereby scraping off the toner of the residual developing liquid. At the same time, the cleaning roller absorbs the toner and carrier liquid. The cleaning blade scrapes off the developing liquid that the cleaning roller failed to remove.
However, even the above-described two cleaning devices sometimes fail to fully remove the residual developing liquid, resulting in defective cleaning. Specifically, when use is made of the dense, viscous developing liquid, the residual liquid remaining on the image carrier after image transfer scarcely contains the carrier liquid and causes the toner to cohere and adhere to the image carrier. In this condition, the cleaning device implemented by the cleaning blade cannot fully scrape off the cohered toner alone. The cleaning roller, even when combined with the cleaning blade, cannot fully scrape off the cohered toner due to its soft surface. This is particularly true when the image carrier is implemented by the intermediate image transfer body. This is because the solid content of the developing liquid increases every time a toner image transferred from the image carrier to the intermediate image transfer body and then to a paper sheet, aggravating the cohesion of the toner on the transfer body.
While the problem discussed above is apt to arise particularly in an image forming apparatus using a dense, viscous developing liquid, it is likely to arise in any image forming apparatus so long as it uses a developing liquid.
To remove toner entered pits existing in the surface of the image carrier, the cleaning blade has customarily been pressed against the image carrier by a high pressure (or by a great amount of bite when the image carrier is a belt) Such a pressure or an amount of bite, however, is apt to increase the drive load of the image carrier, affecting the drive of the image carrier while bringing about noise and the deformation of the cleaning blade. In addition, the above pressure or the amount of bite causes the wear and damage of the cleaning blade itself. For this reason, the pressure or the amount of bite of the cleaning blade is limited, so that the cleaning effect available with the blade scheme is limited. This is also true with an image forming apparatus using a dry powdery developer, which will be described later.
Japanese Patent Laid-Open Publication No. 9-230771 proposes an image forming apparatus including developing means using a developing liquid and cleaning means assigned to a photoconductive element or image carrier. The cleaning means is implemented by a cleaning blade, a foam roller located downstream of the blade in the direction of rotation of the photoconductive element, and liquid feeding means for feeding a cleaning liquid to the foam roller. The cleaning liquid is fed to the photoconductive element via the foam roller in order to remove the developing liquid left on the drum in such a manner as to wash it away. Further, the cleaning liquid wets toner cohered on the photoconductive element and thereby helps the foam roller and cleaning blade remove the toner. In addition, the cleaning liquid washes away toner entered the pits of the photoconductive element and causes toner to rise above the pits, facilitating the removal of the toner. In this manner, the cleaning means cleans the photoconductive element with an improved ability.
The above-described cleaning means using a cleaning liquid cleans a photoconductive element or image carrier with an improved ability. The above document, however, does not give any consideration to the defective cleaning of an intermediate image transfer body.
In an image forming apparatus using a dry powdery developer, a cleaning device removes toner left on an image carrier, which is a photoconductive element or an intermediate image transfer body, after image transfer. The cleaning device is implemented by a cleaning blade similar to the cleaning blade of the image forming apparatus using a cleaning liquid. The cleaning blade may be combined with a rotatable bias roller located downstream of the cleaning blade in the direction of rotation of the image carrier and facing the image carrier. This kind of cleaning device is taught in, e.g., Japanese Patent Laid-Open Publication No. 11-38777. In the cleaning device using both of the cleaning blade and bias roller, a voltage of preselected polarity is applied to the bias roller in order to form an electric field between the image carrier and the bias roller. The electric field causes toner charged to the opposite polarity to the above voltage to move toward the bias roller. Consequently, the toner, which the cleaning blade failed to remove, moves toward the cleaning member away from the image carrier on the basis of electrophoresis.
However, the current trend in the imaging art is toward toner having a smaller particle size and a more spherical shape. The probability that such toner contacts the cleaning member is low and apt to lower the cleaning ability. In these circumstances, there is an increasing demand for a higher cleaning ability even with an image forming apparatus of the type using a dry powdery developer.
It is therefore an object of the present invention to provide an image forming apparatus capable of cleaning an image carrier with an unprecedented ability.
In accordance with the present invention, an image forming apparatus includes a developing device using a developing liquid consisting of a carrier liquid and toner dispersed in the carrier liquid. An image carrier carries a toner image developed by the developing device. A cleaning verb r cleans the surface of the image carrier after the toner image has been transferred from the image carrier to a recording medium. A liquid feeding device feeds a cleaning liquid to the cleaning member The image carrier is implemented as an intermediate image transfer body for carrying the toner image transferred thereto from another image carrier. The toner image is transferred from the intermediate image transfer body to the recording medium.
Also, in accordance with the present invention, an image forming apparatus includes a developing device using a developing liquid consisting of a carrier liquid and toner dispersed in the carrier liquid. An image carrier carries a toner image developed by the developing device. A cleaning member cleans the surface of the image carrier after the toner image has been transferred from the image carrier to a recording medium. A liquid feeding device feeds a cleaning liquid to the surface of the image carrier after the surface has moved away from an image transfer position, but before it reaches the cleaning member. The image carrier is implemented as an intermediate image transfer body for carrying the toner image transferred thereto from another image carrier. The toner image is transferred from the intermediate image transfer body to the recording medium.
Further, in accordance with the present invention, an image forming apparatus includes a developing device using a powdery developer containing at least toner. An image carrier carries a toner image developed by the developing device. A cleaning member cleans the surface of the image carrier after the toner image has been transferred from the image carrier to a recording medium. A liquid feeding device feeds a cleaning liquid to the cleaning member.
Moreover, in accordance with the present invention, an image forming apparatus includes a developing device using a powdery developer containing at least toner. An image carrier carries a toner image developed by the developing device. A cleaning member cleans the surface of the image carrier after the toner image has been transferred from the image carrier to a recording medium. A liquid feeding device feeds a cleaning liquid to the surface of the image carrier after the surface has moved away from an image transfer position, but before it reaches the cleaning means.
In addition, in accordance with the present invention, an image forming apparatus includes a developing device using a developing liquid consisting of a carrier liquid and toner dispersed in the carrier liquid. An image carrier carries a toner image developed by the developing device. A cleaning member cleans the surface of the image carrier after the toner image has been transferred from the image carrier to a recording medium. An electric field forming device forms an electric field, which causes the toner of the residual developing liquid remaining on the image carrier to move toward the surface of the cleaning member, between the image carrier and the cleaning member.